1. Field of the Invention
The present invention relates to an optical switch used for switching of an optical path in an optical communication equipment.
2. Description of the Background Art
A conventional optical switch 100 will be described with reference to FIG. 13. This optical switch 100 is one shown in TuM1 (J. E. Fouquet, xe2x80x9cCompact optical cross-connect switch based on total internal reflection in a fluid-containing planar lightwave circuitxe2x80x9d) at OFC 2000 (Optical Fiber communication Conference, Mar. 7, 2000). Optical switch 100 is formed by a silica planar optical circuit substrate 51, where a two-dimensional optical circuit is formed by providing a rectangular optical waveguide having a slightly high refractive index within silica planar optical circuit substrate 51. Generally, silica planar optical circuit substrate 51 having a refractive index of about 1.5 is employed, while optical waveguide 2 portion is made of a material with a refractive index that is higher by about 1%. The portion of optical waveguide 2 is in general also referred to as a xe2x80x9ccore.xe2x80x9d A trench 52 is formed such that it traverses a position that partially overlaps with a crosspoint of optical waveguides 2, and trench 52 is filled with refractive index-matching oil 56. Refractive index-matching oil 56 is oil having a refractive index equal to that of optical waveguide 2.
An operation of optical switch 100 will be described. In optical switch 100, a bubble generating mechanism, not shown, is provided which can generate a bubble 53 and also make bubble 53 disappear in the liquid of refractive index-matching oil 56 at a crosspoint of optical waveguides 2. For the bubble generating mechanism, the same mechanism as that used for a head of a bubble-jet printer may be employed.
When bubble 53 is generated at a crosspoint, a light that enters into the crosspoint is totally reflected by a surface of bubble 53, while when no bubble 53 exists, the light travels in a straight line because optical waveguide 2 and refractive index-matching oil 56 have an equal refractive index. By utilizing this property, an optical path can be switched between two states of reflection/straight travel by generation/disappearance of bubble 53.
In optical switch 100 formed in the above-described manner, accuracy of an etching process requires a width of trench 52 to be at least about 15 xcexcm. In addition, there is a problem of optical loss of at least 0.07 dB per crosspoint. On the other hand, optical loss L [dB] of optical switch 100 as a whole is given by the following formula:
L=2C+(mxe2x88x921)T+(nxe2x88x921)T+R,
where
m is a number of input ports,
n is a number of output ports,
C is a loss [in dB] upon entry of a light into an optical switch from an optical fiber and during travel through an optical waveguide to an active area which is a crosspoint,
T is a loss [in dB] upon traversing one trench and during transmission through a section of a short optical waveguide between two crosspoints, and
R is a loss [in dB] for reflection upon a sidewall of an empty trench and transmission through a section of a short optical waveguide between two crosspoints.
For instance, when configuring a large-scale 1000xc3x971000 optical switch, specific numerical values substituted into the above formula give L=2xc3x970.25+(1000xe2x88x921)xc3x970.07+(1000xe2x88x921)xc3x970.07+2.1=142.46 dB. Thus, even with an ideally produced optical switch, optical loss of 142.46 dB would occur. It is necessary to limit optical loss L to 10 dB or below in order for an optical switch to function without degrading signal quality. In this manner, there is a disadvantage in that a larger scale than about 32xc3x9732 is difficult to form with such type of configuration when optical loss is considered.
Moreover, silica planar optical circuit substrate 51 is produced by a device similar to that which produces a semiconductor so that a large optical switch would disadvantageously become extremely expensive to produce. Further, since bubble 53 is produced and utilized each time it is needed in refractive index-matching oil 56, there is a problem of optical switching malfunction occurring when the generated bubble 53 is too small or when the bubble is generated out of position. Furthermore, depending on the condition of refractive index-matching oil 56, local absorption of light would take place with a small globule of refractive index-matching oil 56 such that an optical path in its periphery would disadvantageously burn due to the energy of a signal light.
It is, therefore, an object of the present invention to provide an optical switch that facilitates production, that can be formed in large scale with little optical loss, and that does not involve switching malfunction or burning as described above.
To achieve the above object, an optical switch according to the present invention includes a plate material basically made of polymer and a drive element. The plate material has optical waveguides that extend linearly within the plate material and a cut provided such that it traverses the optical waveguides, and the drive element selects a path of light by reducing and increasing the gap of the cut.
By adopting the above-described arrangement, the distance of a gap can be switched between being as narrow as xc2xc the wavelength of a signal light or narrower and being wider than xc2xc the wavelength by reducing and increasing the gap of a cut so that switching between connection/reflection of the signal light can be performed. With this type, accuracy with which a gap is controlled may be low so that an optical switch can be formed in a simple manner.
According to the present invention, the cut preferably is cut in from one side of the plate material and is a path selective slit that does not reach the other side of the plate material. By adopting this arrangement, misalignment of optical waveguides can be prevented since a portion of the plate material remains connected.
According to the present invention, the optical waveguides cross one another inside the plate material, and the cut is arranged such that it transverses a crosspoint of the optical waveguides. By adopting this arrangement, switching between connection/reflection at a crosspoint can be effected so that a direction of a signal light can be selected as either of the optical paths at the crosspoint.
According to the present invention, the optical waveguides preferably cross one another inside the plate material, and the cut is arranged such that it transverses a plurality of crosspoints of the optical guides, and the path selective slit extends linearly such that it traverses a plurality of the crosspoints, and plate material has a stress release slit that crosses the path selective slit between one of the crosspoints and another of the crosspoints.
According to the present invention, the drive element preferably is a pressuring element for pressing the cut from one side, and a gap of the cut is reduced to a distance that is xc2xc a wavelength of light propagating a signal or less by pressing effected by a pressuring element. By adopting this arrangement, optical waveguides can be connected by pressing effected by a pressuring element so that a signal light can be transmitted as it is.
According to the present invention, the drive element preferably is a pressuring element for pressing the cut from one side, and a gap of the cut is increased to a distance that is greater than xc2xc a wavelength of light propagating a signal by pressing effected by a pressuring element. By adopting this arrangement, optical waveguides can be blocked by pressing effected by a pressuring element so that a signal light cannot be transmitted and is totally reflected. With this type, the natural form of optical waveguides with substantially no local deformation can be maintained upon transmission so that optical loss during transmission can be reduced.
According to the present invention, the plate material preferably includes a plate-like supporting member having a recessed portion on a surface opposite to the side on which exists a location pressed by the pressuring element. By adopting this arrangement, a plate material can be displaced even with a weak force. Thus, switching between connection/reflection of optical waveguides can be performed with little driving force.
According to the present invention, the pressuring element preferably is a member that can be advanced and retracted along a direction substantially perpendicular to the plate material. By adopting this arrangement, the selection of whether or not to press a plate material by advancement or retraction of a member becomes possible, which facilitates control.
According to the present invention, the pressuring element preferably is a coil formed on a surface of the plate material, a magnet provided in the vicinity of the coil, and a current supply element for supplying a current to the coil. By adopting this arrangement, electrical switching between connection/reflection at each crosspoint can be achieved with a simple mechanism.
According to the present invention, the pressuring element preferably is a balloon-like member which is disposed in contact with the plate material and which can be expanded and contracted. By adopting this arrangement, switching between connection/reflection of optical waveguides can be performed with a very small structure.
According to the present invention, the drive element preferably includes a wedge-shaped member that can be inserted into the cut, and a gap of the cut is increased to a distance that is greater than xc2xc a wavelength of a light propagating a signal by inserting the wedge-shaped member into the cut. By adopting this arrangement, switching between connection/reflection of an optical switch can be effected with a smaller energy than that required in a case where a push rod or a coil is used.
According to the present invention, refractive index-matching oil is preferably applied on a surface exposed inside the cut. By adopting this arrangement, optical loss during connection of optical waveguides can be further reduced.
According to the present invention, the drive element preferably includes a bending element that can block passage of a signal light within the optical waveguides by bending one side to a larger extent than the other side, the one side and the other side having the cut located therebetween along the optical waveguides. By adopting this arrangement, one of the optical waveguides can be bent to a large extent so as to deflect it completely from the path of the other optical waveguide such that no signal light would leak into the optical waveguide that is not the one having light entering into it. Thus, loss can be reduced.
To achieve the above object, a method of producing the optical switch according to the present invention in which a plate material basically made of polymer and a drive element are provided, the plate material having optical waveguides that extend linearly within the plate material and a cut provided such that it traverses the optical waveguides, and the drive element selecting a path of light by reducing and increasing a gap of the cut, includes a slit forming step for providing a slit in the plate material by applying a cutting edge of a cutting tool against the plate material and moving the cutting edge along a direction in which a slit is to be formed while applying a pulling force in a direction perpendicular to the direction in which a slit is to be formed in a plane formed by the plate material.
By adopting the above-described method, a cross section having an orderly alignment on a molecular level can be obtained with a simple operation. As a result, the adhesion upon connection improves, and an optical switch with small optical loss during connection can be obtained.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.